This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2000-364527 filed on Nov. 27, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a diagnosis apparatus for detecting an abnormal state of an evaporation gas purge system in which an evaporation fuel gas generated in a fuel tank is purged to an intake pipe of an internal combustion engine.
2. Description of Related Art
In a conventional evaporation gas purge system, to prevent an evaporation gas generated in a fuel tank from leaking into an atmosphere, the evaporation gas is adsorbed via an evaporation passage in a canister and, then, the evaporation gas adsorbed in the canister is purged via a purge passage to an intake pipe by regulating an opening and closing timing of a purge control valve provided in the purge passage according to operating conditions of an internal combustion engine so that a purge amount of the evaporation gas from the canister to the intake pipe is controlled. It is necessary to detect a leakage of the evaporation gas as soon as possible not to ignore an abnormal state that the evaporation gas leaks from the evaporation gas purge system to the atmosphere for a long time.
According to a conventional diagnosis apparatus, an evaporation gas purge system line is completely closed during a given time period in such a manner that an atmosphere change over valve closes a conduit communicating with atmosphere and, after the purge control valve is once opened so as to introduce negative pressure from the intake pipe to the fuel tank, the purge control valve is closed. A pressure sensor provided in the fuel tank detects a change amount of the pressure inside the fuel tank (tank internal pressure change amount) during the given time period when the evaporation gas purge system line is completely closed. Whether or not the gas leakage occurs in the evaporation gas purge system line is detected by comparing the tank internal pressure change amount with a threshold value for determination. According to the conventional method, unless the gas leakage occurs in the evaporation gas purge system line, the tank internal pressure change amount during the given time period, which is a value corresponding to a generation amount of the evaporation gas, is lower than the threshold value and, if the gas leakage occurs, the tank internal pressure change amount after the negative pressure is introduced, which increases by a value corresponding to the gas leakage, is higher than the threshold value.
According to the conventional diagnosis apparatus, the abnormal state of the evaporation gas purge system is detected under an assumption that the purge control valve and the atmosphere change over valve are always accurately operated. However, there is a possibility that each operation of the purge control valve and the atmosphere change over valve becomes abnormal. If the operation of the purge control valve or the atmosphere change over valve is abnormal, the leakage can not be accurately detected.
To cope with this problem, as disclosed in Japanese Pat. No. 3036703, a diagnosis method is proposed in which the purge control valve is judged to be abnormal unless a given value of the negative pressure is introduced into the fuel tank at a time of the negative pressure introduction. However, abnormal causes why the negative pressure is not accurately introduced into the fuel tank are not only due to the abnormal operation of the purge control valve but also due to the abnormal operation of the atmosphere change over valve or due to an aperture or gap, through which gas leaks, incidentally made in the evaporation gas purge system line. Therefore, according to this diagnosis method, the purge control valve whose operation is normal is sometimes misjudged as abnormal.
An object of the invention is to provide a diagnosis apparatus for detecting an abnormal state of an evaporation gas purge system in which, when an abnormality occurs in the evaporation gas purge system line, its abnormal cause is identified.
To achieve the above object, a diagnosis apparatus for detecting an abnormal state of an evaporation gas purge system line has a passage connecting between a fuel tank and an intake pipe for an internal combustion engine, a canister disposed in the passage for adsorbing evaporation fuel gas from the fuel tank, a purge control valve for controlling a purge of the evaporation fuel gas from the canister to the intake pipe and an atmosphere change over valve for opening and closing an atmosphere communication hole of the canister.
The diagnosis apparatus has pressure detecting means for detecting a tank internal pressure of the fuel tank and abnormal state detecting means for judging an existence of the abnormal state by detecting a fact that, when the purge control valve is opened to introduce a negative pressure from the intake pipe to the fuel tank via the passage in a state that the atmosphere change over valve is closed, the tank internal pressure detected by the pressure detecting means does not decrease up to a given negative pressure at a time when a given time has lapsed after opening the purge control valve. The diagnosis apparatus further has abnormal cause determining means for identifying the at least one of abnormal causes based on the tank internal pressure detected by the pressure detecting means when the existence of the abnormal state thereof is judged by the abnormal state detecting means.
With the diagnosis apparatus mentioned above, at least one of abnormal causes may be identified among a valve closing lock of the purge control valve, a valve opening lock of the atmosphere change over valve and a large amount leakage that the evaporation fuel gas leaks to atmosphere from a portion other than the atmosphere communication hole.
As an alternative, the diagnosis apparatus may have pressure detecting means for detecting a tank internal pressure of the fuel tank and abnormal state identifying means. The abnormal state identifying means determines the abnormal state as the valve closing locking of the purge control valve, if the tank internal pressure detected by the pressure detecting means increases, when the purge control valve is opened to introduce a negative pressure from the intake pipe to the fuel tank via the passage in a state that the atmosphere change over valve is closed.
It is preferable that the abnormal cause determining means has calculation means calculating a change amount of the tank internal pressure during a given period or calculation means calculating an integration value of the tank internal pressure during another given period, and comparing means for comparing the change amount or the integration value with at least one of threshold values so that at least one of the abnormal causes is identified.
Preferably, the change amount or the integration value is calculated when the, internal combustion engine is operated in a driving range in which the purge control valve is intermittently opened to intermittently purge the evaporation fuel gas from the canister to the intake pipe in a state that the atmosphere change over valve is opened.
The comparing means determines the abnormal cause as the valve closing state locking of the purge control valve when the change amount is not larger than a first given value representing the at least one of threshold values or when the integration value is not smaller than a second given value representing the at least one of threshold values.
Further, the comparing means determines the valve opening state locking of the atmosphere change over valve when the change amount is larger than a third given value among the threshold values, which is larger than the first given value, or when the integration value is smaller than a fourth given value among the threshold values, which is smaller than the second given value.
Moreover, the comparing means determines the large amount leakage when the change amount is larger than the first given value but is not larger than the third given value or when the integration value is not smaller than the fourth given value but smaller than the second given value.